Dampened railway car truck

ABSTRACT

A four-wheel, two-axle railway car truck having non-integral side frames, a spring plank and a bolster, functioning both as a swing motion truck and a roll control truck and having its side frames journaled on the associated wheel and axle assemblies for swinging movement of the side frames transversely of the truck. The truck has a first stop means on the bolster for restricting the lateral movement of the bolster relative to the side frames at a level below the plane containing the longitudinal axes of the axles and second stop means associated with the spring plank and side frames for limiting the swinging movement of the side frames.

United States Patent Weber et a].

[ June 20, 1972 [54] DAMPENED RAILWAY CAR TRUCK [72] lnventors: Hans B. Weber, Bedford; Joseph Brown,

Warrensville Heights, both of Ohio [73] Assignee:

[521' U.S.Cl. ..105/17l, 105/182 R, 105/193, 105/197 D, 105/201, 105/206 R, 105/208,

[51] Int. Cl ..B61f5/06,B61f5/12,B61f5/38 [58] Field ofSearch ..105/182,185,186,187,188, IDS/189,192,193, 197,197 D, 198, 201, 202, 203,

2,044,971 6/1936 Clasen ..105/208 2,387,072 10/1945 Holland et a1. .,105/185 2,717,558 9/1955 Shafer ....l05/l93 X 2,737,907 3/1956 Janeway.... 105/197 X 2,740,360 4/1956 Janeway.... ....105/l93 X 2,746,744 5/1956 Blattner .105/197 D X 3,461,8l4 8/1969 Weber et al. ..l05/193 Primary ExaminerArthur L. La Point Assistant Examiner-l-loward Beltran Attorney-l-lenry Kozak and Woodrow W. Portz {5 7] ABSTRACT A four-wheel, two-axle railway car truck having non-integral side frames, a spring plank and a bolster, functioning both as a swing motion truck and a roll control truck and having its side frames journaled on the associated wheel and axle assemblies for swinging movement of the side frames transversely of the truck. The truck has a first stop means on the bolster for restricting the lateral movement of the bolster relative to the side frames at a level below the plane containing the longitudinal axes of the axles and second stop means associated with the spring plank and side frames for limiting the swinging movement of the side frames.

1 1 Claims, 14 Drawing Figures DAMPENED RAILWAY CAR TRUCK BACKGROUND OF THEINVENTION Two major problems confront railroads today in freight operations where standard railway freight car trucks are in use. One of these problems is lateral instability due to truck hunting at high speed. High speed in this instance means a speed in excess of approximately 55 miles per hour for A.A.R. approved commercial railway freight car trucks. The other problem is car roll for high capacity, high center of gravity railway cars.

Truck hunting causes the rolling wheels and axle assembly of a standard railway freight car truck to move along a pair of rails in a sinusoidal pattern. That is, the rolling wheels and axle assembly first turn toward one rail and then toward the opposite rail as the railway vehicle moves along the track. Thus, as the periodic motion continues, it creates a sinusoidal wave pattern. In stable or controlled truck hunting, the amplitude of this periodic lateral motion is relatively small and wheel flange contact with the rails is generally avoided. Truck hunting, however, becomes harmful at high speedswhen resonance occurs and when that resonance cannot be controlled. That is, at high speeds the wave pattern of the wheel and axle assembly can have the same frequency as the natural roll, sway, and yaw frequencies of the car body. If the resultant lateral disturbance of thecar truck is large enough and in resonance with the natural frequencies of the sprung car body, violent lateral forces are created which act upon boththe car trucks and car body to sustain the resonance. Those lateral forces resulting from uncontrolled hunting cause: (1) transverse sliding of the wheels on the rails, (2) heavy lateral impacts between wheel flanges and rails, (3) rail damage, (4) excessive wear to truck and car body component parts, and (5) lading damage.

Just as uncontrolled truck hunting is critical at high speeds, harmonic car roll is a critical problem at low speeds. With the introduction of high capacity, high center of gravity cars a few years ago, it was noted that as these cars moved over a section of track having low, staggered rail joints, the cars rocked so violently that they derailed. This derailment problem is generally experienced with the above-mentioned cars which have a longitudinal spacing between the car truck centers approximately equal to the rail length, and either when the loaded cars are operated at a running speed between and miles per hour or when empty cars are operated at a running speed between 30 and 40 miles per hour over a series of low rail joints. This combination results in excessive car roll, causing wheel unloading and wheel lift, or climb, especially on curved track.

Applicant has effectively minimized the car roll problem and derailment tendencies of rocking, high capacity, high center of gravity cars by using a Roll Control" mechanism, which mechanism is described in applicant's co-pending patent application Ser. No. 621,225, filed Mar. 7, 1967 now U.S. Pat. No. 3,461,814. Briefly, incorporation of the R011 Control" feature in a standard railway freight car truck is aceomplished by interconnecting the side frames of the truck with a spring plank at the level of the load support spring seats, and by providing lateral stops between the spring plank and bolster at the level of the spring plank. As a result, the point of application of the lateral forces is lowered from the height of the conventional bolster gibs (which are eliminated in the Roll Control" truck) to the height of the bottom portion of the bolster opening on the side frames. Accordingly, the overturning moment of the truck caused by the lateral roll forces which had previously tended to cause wheel unloading and wheel lift is substantially reduced.

SUMMARY OF THE INVENTION The invention as described hereinafter is a modification of the Roll Control" truck since it incorporates many of its essential features. The improved railway car truck design is based upon the swing motion principle which permits limited Swinging movement of the side frames on the adapters disposed within the pedestal jaws of the side frames. Once the swinging motion of the side frames is stopped, the truck functions as the Roll Control truck.

Applicant has modified his Roll Control" truck by incorporating a rocker seat between each side frame and the spring plank. The rocker seat permits the side frames to swing in unison as pendulums, or swing hangers, in either direction laterally of the truck. Swinging of the side frames is stopped prior to the engagement of the lateral stops provided between the bolster and spring plank by contact between the side frame tension member (formerly the load support spring seat) and the rocker seat. In this manner, increased lateral motion of the bolster relative to the side frame is obtained. Since lateral motion initially results from partial transverse deflection of the load springs and from the swinging of the side frames and subsequently solely by the deflection of the load springs, the resulting lateral force-travel curve characteristic defining the resistance to lateral motion of the bolster relative to the side frames is non-linear. This non-linear lateral characteristic is significant in the attainment of improved high speed truck perforrnance. It improves lateral ride; minimizes lateral disturbances of the sprung car body due to truck hunting; reducesthe critical speed for hunting in combination with car body roll, sway and yaw; acts as a resonance arrester; permits controlled and safe ride qualities while passing through the critical speed ranges; cushions lateral impact; reduces wear on wheel flanges, truck and car component parts; reduces rail damage; and minimizes lading damage.

It is therefore an important object of the invention to provide a railway car truck having embodied therein a non-linear lateral force-travel curve characteristic defining the resistance to lateral movement of the bolster relative to the side frame.

It is a further object to provide a car truck for high center of gravity freight car use of the type which incorporates a replaceable rocker seat between the spring plank and side frame to permit swinging of the side frames relative to journal axles.

Another object of this invention is to provide a mechanical interference between the rocker seat and side frame to limit lateral side frame swing.

Yet another object is to provide a railway car truck that is effective in minimizing, (1) car roll and derailment of rocking cars, without special additional anti-roll devices, and (2) lateral disturbance of the sprung car body due to truck hunting.

DESCRIPTION OF THE DRAWINGS In the drawings, with respect to which the invention is described below:

FIG. I is a side elevation, partly in section, of a railway car truck in accordance with the invention;

FIG. la is a vertical sectional view taken along line a-a of FIG. 1, looking in the direction of the arrows with the bearing assembly removed.

FIG. 2 is a fragmentary plan view, partly in section, taken along line 2-2 of FIG. 1;

FIG. 3 is an enlarged fragmentary side elevation, partly in section, illustrating one end of a pivotally supported rocker seat;

FIG. 4 is a fragmentary end view taken along line 44 of FIG. 3;

FIG. 5 is a fragmentary plan view taken along line 5-5 of FIG. 3;

FIG. 6 is a fragmentary end view, partially in section, taken along line 6-6 of FIG. 1;

FIGS. 7 and 8 are views similar to FIG. 6, illustrating lateral motion of the truck during the first and second stages of lateral truck displacement;

FIGS. 9 and 10 are force-travel diagrams which show the characteristic curves for empty and fully loaded cars for the laterally displaced positions shown in FIGS. 7 and 8, respectively;

FIG. 11 is a view similar to FIG. 6 illustrating another embodiment of the invention;

FIG. 12 is similar to FIG. 11 and illustrates the position of the bolster and side frame after full lateral truck displacement; and

FIG. 13 is a partial side elevation view of an alternate friction system for snubbing the vertical and lateral movements of the bolster relative to the side frame.

DESCRIPTION OF THE EMBODIMENT Referring to FIGS. 1 through 8 of the drawings, a snubbed railway car truck is illustrated comprising a side frame having a tension member 21 and a compression member 22. The members merge as at 23 and provide a pedestal jaw 24 for receiving in rockable relation an adapter 25 and bearing assembly 26 of a joumaled wheel and axle assembly 27. A plate member 18 is interposed between jaw 24 and adapter 25. The top side of the adapter 25 is convexly crowned as at 25a and is engaged by the convexly curved undersurface 18a of member 18 to permit swinging movement of the side frame relative to the adapter and the wheel and axle assembly. Intermediate the lengthwise direction'of the frame, there is positioned a pair of spaced vertical columns 28--28. The columns connect the tension and compression members to form and partially define a bolster receiving opening 29. Opening 29 receives one end of bolster 30 arranged with its longitudinal axis transverse to thelength of the frame. It will be understood that while only oneside frame has been shown in the drawings, there is a similar frame on the other side of the car truck which cooperates with the bolster and other parts of the truck in like manner.

Tension member 21 includes a U-shaped base portion 31 for partially housing a rocker seat 32. The rocker seat comprises an elongated plate section 33 and a depending inverted T-shaped strengthening member 34. Each end of the rocker seat has a trunnion member 35 for rockably supporting the rocker seat relative to the side frame. Trunnion members 35- 35 are pivotally supported in a pair of longitudinally spacedapart rocker bearings 36 which are disposed beneath columns 28 and are coaxially aligned in base portion 31 of tension member 21. Each rocker bearing 36 has a concave cylindrical bearing surface 37 having a radius of curvature greater than that of the associated trunnion member 35 pivotally received therein to assure that rocking engagement occurs between the trunnion member and bearing. Rocker seat 32 provides a top surface 38 for supporting a channel shaped end of a spring plank 40 arranged with its longitudinal axis transverse to the length of the frame. Plank 40 is interconnected to rocker seat 32 by upstanding bosses 41 formed on the seat and extending through openings in the plank to interlock the two side frames together; A spring group 42 is disposed between spring plank 40 and bolster 30 for resiliently supporting the end of the bolster.

The bolster illustrated in FIGS. 1 and 2 is generally of boxshaped construction at each end and comprises spaced vertical side walls 45-45, spaced top and bottom walls, 46 and 47, respectively, and a vertical central wall 48 joining the top and bottom walls. A stop lug 50 depends from the bottom wall of the bolster inwardly from each of its ends and is in spaced relation with an upstanding abutment 51 carried by spring plank 40 intermediate its ends. Lug 50 and abutment 51 are spaced apart a predetermined distance so as to provide a clearance between opposing vertical surfaces thereon preferably on the order of approximately five-eighths of an inch, which clearance permits limited lateral movement of the bolster transversely of the truck. It will be seen that the engagement between each lug and abutment will occur at a level substantially below the horizontal plane containing the rockable connection defined by the adapter 25 and pedestal jaw 24, which connection may be of the type disclosed in either U.S. Pat. Nos. 2,7l7,558 or 2,737,907. This form of a connection normally allows the side frames of the truck to swing transversely of the truck.

For snubbing the sprung mass of the railway car truck, each end portion of the bolster has at each side a pocket 55 opening towards the adjacent column 28 for receiving a friction shoe 56. Each pocket has an inclined rear wall 57 which slopes upwardly and outwardly toward the adjacent column 28. Each friction shoe is in wedging engagement between wall 57 and the opposing column 28. Each shoe has a sloping surface 58 engaging surface 60 on wall 57 and a vertical friction surface 59 engaging surface 61 on a wear plate 62 that is secured to the adjacent column. In operation the friction shoe is urged upwardly and outwardly by a spring 63 disposed on plank 40 into frictional engagement with surface 61 of the wear plate to provide resistance to both vertical and lateral movements of the bolster.

Referring to FIGS. 4 and 6 through 10, the operation of the railway car truck will be explained. As mentioned hereinabove, the structural arrangement of the truck parts permits the side frames to swing laterally in unison. Swinging of the side frames in either direction is stopped by contact between undersurface 65 of the rocker plate section 33 and top surface 66 of one of the side walls 6767 of base portion 31 of the tension member. The clearance between these engaging surfaces permits approximately a 3 degree side frame swing in either transverse direction of the side frame from its neutral position as shown in FIG. 6. This swinging movement results in approximately five-eighths inch lateral motion of the bolster in either direction. An additional five-eighths inch lateral motion of the bolster is obtained by the lateral deflection of the load spring, as shown in FIG. 8. FIGS. 9 and 10 graphically illustrate the resulting lateral load deflection characteristic for each distinct stage of lateral movement of the bolster for both empty and fully loaded cars. The empty and loaded car characteristics shown are different because the resistance to lateral motion, as in any swing hanger type railway car truck, is dependent upon the load carried by the bolster. Thus the resistance to lateral motion varies in proportion to the vertical load, and any partial load will result in a curve proportionally located between the curves for the empty and fully loaded car.

During the first stage of lateral movement, as illustrated in FIG. 7, the resistance against side frame swing is influenced basically by three controlling factors (1) the swing hanger length; that is, the vertical distance between the engaging portions of the pedestal jaw 24-adapter 25 and the rocker bearing 36-trunnion 35, (2) the normal forces of gravity acting upon the car body and side frames 20, and (3) the resistance to lateral distortion of the load springv group 42. These controlling factors work together and in series to provide the low resistance portions A and A of the non-linear curves shown in FIG. 9. After the swinging of the side frames has been stopped by the engagement of rocker seat 32 with tension member 21, the remaining lateral motion of the bolster is obtained by the deflection of the load springs 42 as illustrated in FIG. 8, resulting in the second stage or high resistance portions B and B of the non-linear curves shown in FIG. 10. In this manner the non-linear lateral force-travel curve characteristic is obtained and defines the low to high resistance to lateral movement of the bolster relative to the side frame.

The first stage A and A of the non-linear curves shown in FIG. 9 can be best explained in the following manner. Under the theory of vibrations it is known that when a lateral load is applied to a pendulum, the lateral displacement of the pendulum is in proportion to the applied load. This characteristic is similar to that of a spring in tension or compression since when a vertical load is applied to a spring, its deflection is in proportion to the applied load. Therefore, a theoretical spring rate for a spring can be substituted for the lateral force-displacement characteristic of a pendulum. That is, since the side frame functions as a swing hanger or pendulum and moves in the same lateral direction as the laterally distorted load springs 42, the lateral swinging movement of the side frame has an effective spring rate. Further, a helical spring has a lateral forcetravel characteristic in addition to its vertical force-travel characteristic. Therefore, the lateral deflection of the load springs 42 and the lateral deflection of the swing hanger can be considered as two springs acting in series. It is well known that when two springs act in series, the resulting spring rate K is lower thantliat for either of the two springs individually. Thus the low resistance portions A and A of the non-linear curves are basically governed by the formula K, =(K,-K )/(K, K,) where K 1 in this instance is the effective spring rate of the swinging side frame, K, is the lateral spring rate of the load springs 42, and K is the resulting spring rate that defines the resistance to lateral movement of the bolster relative to the side frame. After a predetermined amount of side frame swing, the swinging is stopped and any remaining lateral travel of the bolster relative to the side frame is working solely against the lateral resistance of the load springs 42 which, as previously stated, have a spring rate appreciably stiffer than the first stage.

Each stage of the non-linear lateral force-travel curve has the following effect on the functioning of the present railway car truck. If only the low force-travel characteristic of the first stage was provided, as is known in the art, under large lateral rail irregularities the total available'amount of lateral travel would be absorbed, thereby resulting in heavy lateral contact between any bolster stops and side frame abutment stops provided, such as bolster gibs or bolster safety stops. In addition, a railway vehicle negotiating super-elevated curves would move laterally the total available amount until contact is made between whatever stops are provided between the bolster and side frame. The vehicle would remain in this laterally displaced position until it traverses the super-elevated curve; thus causing a poor lateral ride.

Considering only the second stage or high resistance portion of the curve, the lateral characteristic is substantially the same as that obtained from the load springs in conventional trucks. This conventional suspension system is not capable, due to its high lateral resistance, of avoiding uncontrolled hunting or lateral instability in the railway vehicle. As noted from FIGS. 9 and 10, the total available built-in lateral motion in either lateral direction is approximately 1 /4 inches. As can be seen from the curves, the low resistance or first stage has a lateral deflection characteristic of approximately three-fourths of an inch. This 34 inch lateral capability is suflicient to absorb the normal lateral disturbances caused by normal lateral rail irregularities plus normal lateral amplitudes of the sinusoidal wave pattern producedby the running wheels and axle assembly. These'normal lateral disturbances result in approximately '15 inch lateral travel, in either direction, from the track centerline. Since these normal lateral disturbances are within the it inch low resistance portion of the curve, the forces transmitted into the car body are substantially reduced. These reduced forces are easily damped by a snubbing system, such as described hereinabove.

If the railway vehicle has to negotiate large lateral disturbances, such as turn-outs and crossings, high lateral forces are encountered. After the first stage of the non-linear curve absorbs a portion of these lateral forces, the remaining lateral forces resulting from the large lateral disturbance will be cushioned by the high resistance portion of the stifier second stage. This mode of operation eifectively reduces wheel flange contact between the rail and wheel and minimizes wear on component parts of the truck and car body.

Referring now to FIGS. 11 and 12, there is illustrated a modified rocker connection between tension member 71 of a side frame 72 and a spring plank 73. Briefly, a rocker bearing plate 74 having a predetermined upwardly facing convex contour 75 in the transverse direction of the side frame is secured to tension member 71. Plate 74 receives in supporting rockable relation one end of the spring plank 73 having a horizontal bearing plate 76 attached to the plank for engagement with plate 74. A pair of spaced flanges 77 -77 extend downwardly from the underneath portion of the spring plank to define a pair of surfaces 78-78 in flanking relation with cooperating side frame surfaces 79-79. Flanges 7777 are in close spaced relationship to surfaces 79-79 to thereby interconnect the plank with the side frame and prevent any longitudinal movement of the plank relative to the side frame. Swinging of the side frame in either direction is stopped by contact between the underneath surface 81 of plate 76 with the predetermined sloping contour 75 of plate 74. The wedge shaped clearance 83 defined between the engaging portions of the two plates permits an approximate three degree side frame swing in either transverse direction of the side frame and results in approximately five-eighths of an inch lateral movement of bolster M in either direction. Ifdesired, surfaces 78- 78 may be tapered downwardly and away from each other to present a pair of sloping surfaces that define a wedge shaped clearance between the sloping surfaces and the cooperating surfaces 79-79 of tension member 71. Accordingly, the swinging of the side frame could then be stopped by the engagement of these cooperating surfaces.

H6. 13 illustrates an alternate friction system well known in the railway art and comprises the conventional friction shoe 91 housed in a pocket 92 of the side frame column 93. A spring 94 urges the friction shoe downwardly into frictional engagement with a wear plate 95 secured to the bolster 96 to snub the vertical and lateral movements of the bolster relative to the side frame.

Summarizing, the present railway car truck provides a moderate total amount of lateral movement approximately equal to 1% inches to either side of the railway track centerline. The truck further combines: (l) the feature of a low resistance to normal lateral movement of the bolster relative to the side frame for avoiding uncontrolled hunting, with (2) the feature of a stiffer resistance to any excessive lateral movement of the bolster for avoiding heavy lateral contact between the bolster stops and associated parts of the side frame.

We claim:

1. in a railway car truck comprising a pair of side frames rockably journaled on associated wheel and axle assemblies for lateral swinging movement under the action of laterally directed forces applied to the truck, each frame comprising a tension member having a base portion and a pair of vertical columns extending upwardly from the base portion and spaced in the lengthwise direction of the frame to define a bolster opening, a spring plank extending between said frames with each end of said plank being received in said opening of the adjacent frame, rocker means between each end of said plank and said base portion of each frame for supporting said plank for rocking movement in a direction laterally of said frames, means interconnecting the ends of said plank and said frames to interlock said frames to the plank, a bolster extending between said frames and supported at its ends within the bolster opening of the adjacent frame, spring means on said plank within each opening for supporting said bolster end first stop means on said bolster and plank adapted to engage upon a predetermined amount of lateral swinging movement of said frames and transverse deflection of said spring means to limit the lateral movement of said bolster relative to said frames, said stop means engaging at a point below the plane containing the axes of the axles and a friction shoe interposed between and resiliently urged into engagement with a side of said bolster and the opposing one of said columns for frietionally resisting movement of said bolster; the improvement comprising: second stop means associated with each end of the spring plank and engageablewith stop means on said base portion of the side frames for limiting said predetermined amount of swinging movement of the side frames in either direction from the central longitudinal vertical plane of the side frame prior to the engagement of said first stop means, said first and second stop means establishing a non-linear, lateral forcetravel curve comprising a first stage and a second stage defining the resistance to lateral movement of said bolster relative to said side frame.

2. The car truck as in claim 1 in which said second stop means comprises engageable opposing surfaces on said rocker means and on said base portion.

3. The car truck as in claim 1 in which each end of said plank is formed with a pair of depending flanges disposed in close overlapping relationship with the sides of said base portion to tie said side frames to said plank.

4. The car truck as in claim 1 in which the lateral swinging movement of said side frames and the transverse deflection of said spring means act jointly prior to the engagement of said second stop means and define said first stage of said curve wherein low resistance to lateral movement of said bolster relative to said side frames occurs.

5. The car truck as in claim 1 in which the transverse deflection of said spring means after the engagement of said second stop means and prior to the engagement of said first stop means defines said second stage of said curve wherein high resistance to lateral movement of said bolster relative to said side frames occurs.

6. The car truck as in claim 1 in which the swinging movement of said side frames is limited by said second stop means to approximately 3 degrees in either direction.

7. The car truck as in claim 1 wherein each frame has a compression member and a tension member joined by said spaced vertical columns and in which said base portion of said tension member defines the bottom of said bolster opening and said spaced columns define the opposite sides of said bolster opening; said rocker means comprising an elongated plate section connected to said base portion of said tension member between said columns centrally along the longitudinal vertical plane of the side frame.

8. The car truck as in claim 7 in which said elongated plate section has a trunnion member on each end of the plate for pivotably supporting the plate, and said base portion of said tension member has a pair of bearings spaced in the lengthwise direction of the frame adapted to receive said trunnion members for pivotal movement of the plate about a longitudinal axis disposed within the vertical plane of the side frame.

9. The car truck as in claim 8 in which said base portion of said tension member is U-shaped in cross section and said second stop means comprises opposing surfaces on said U- shaped portion of said tension member and said plate section.

10. The car truck as in claim 7 in which said plate section has an upwardly facing surface of convex contour in the transverse direction of the side frame for receiving in supporting rockable relation said end of said spring plank.

11. The car truck as in claim 10 in which said second stop means comprises opposing surfaces on said plate section and said spring plank. 

1. In a railway car truck comprising a pair of side frames rockably journaled on associated wheel and axle assemblies for lateral swinging movement under the action of laterally directed forces applied to the truck, each frame comprising a tension member having a base portion and a pair of vertical columns extending upwardly from the base portion and spaced in the lengthwise direction of the frame to define a bolster opening, a spring plank extending between said frames with each end of said plank being received in said opening of the adjacent frame, rocker means between each end of said plank and said base portion of each frame for supporting said plank for rocking movement in a direction laterally of said frames, means interconnecting the ends of said plank and said frames to interlock said frames to the plank, a bolster extending between said frames and supported at its ends within the bolster opening of the adjacent frame, spring means on said plank within each opening for supporting said bolster end first stop means on said bolster and plank adapted to engage upon a predetermined amount of lateral swinging movement of said frames and transverse deflection of said spring means to limit the lateral movement of said bolster relative to said frames, said stop means engaging at a point below the plane containing the axes of the axles and a friction shoe interposed between and resiliently urged into engagement with a side of said bolster and the opposing one of said columns for frictionally resisting movement of said bolster; the improvement comprising: second stop means associated with each end of the spring plank and engageable with stop means on said base portion of the side frames for limiting said predetermined amount of swinging movement of the side frames in either direction from the central longitudinal vertical plane of the side frame prior to the engagement of said first stop means, said first and second stop means establishing a non-linear, lateral force-travel curve comprising a first stage and a second stage defining the resistance to lateral movement of said bolster relative to said side frame.
 2. The car truck as in claim 1 in which said second stop means comprises engageable opposing surfaces on said rocker means and on said base portion.
 3. The car truck as in claim 1 in which each end of said plank is formed with a pair of depending flanges disposed in close overlapping relationship with the sides of said base portion to tie said side frames to said plank.
 4. The car truck as in claim 1 in which the lateral swinging movement of said side frames and the transverse deflection of said spring means act jointly prior to the engagement of said second stop means and define said first stage of said curve wherein low resistance to lateral movement of said bolster relative to said side frames occurs.
 5. The car truck as in claim 1 in which the transverse deflection of said spring means after the engagement of said second stop means and prior to the engagement of said first stop means defines said second stage of said curve wherein high resistance to lateral movement of said bolster relative to said side frames occurs.
 6. ThE car truck as in claim 1 in which the swinging movement of said side frames is limited by said second stop means to approximately 3* in either direction.
 7. The car truck as in claim 1 wherein each frame has a compression member and a tension member joined by said spaced vertical columns and in which said base portion of said tension member defines the bottom of said bolster opening and said spaced columns define the opposite sides of said bolster opening; said rocker means comprising an elongated plate section connected to said base portion of said tension member between said columns centrally along the longitudinal vertical plane of the side frame.
 8. The car truck as in claim 7 in which said elongated plate section has a trunnion member on each end of the plate for pivotably supporting the plate, and said base portion of said tension member has a pair of bearings spaced in the lengthwise direction of the frame adapted to receive said trunnion members for pivotal movement of the plate about a longitudinal axis disposed within the vertical plane of the side frame.
 9. The car truck as in claim 8 in which said base portion of said tension member is U-shaped in cross section and said second stop means comprises opposing surfaces on said U-shaped portion of said tension member and said plate section.
 10. The car truck as in claim 7 in which said plate section has an upwardly facing surface of convex contour in the transverse direction of the side frame for receiving in supporting rockable relation said end of said spring plank.
 11. The car truck as in claim 10 in which said second stop means comprises opposing surfaces on said plate section and said spring plank. 